The present disclosure relates generally to information handling systems (IHSs), and more particularly to a soft start circuit with an active reset for an IHS.
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option is an information handling system (IHS). An IHS generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes. Because technology and information handling needs and requirements may vary between different applications, IHSs may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in IHSs allow for IHSs to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, IHSs may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Traditionally, portable IHSs have been configured to receive electrical power from either an AC power adaptor or a battery. More recently portable IHSs are configured to also receive electrical power from an inductive wireless power/charger devices. Inductive wireless power/charger devices can transfer electrical power to the IHS inductively when in a near proximity to the IHS power receiving circuit. Switching between power sources on the IHS can lead to current spikes on the power rail of the IHS when one source is removed and the other source is applied, which can damage the IHS. To prevent current spikes on the electrical power rail, these IHSs are generally designed to slowly transition between the different power sources, using a soft start power transition circuit. The soft start circuit ramps down power from one power source and ramps up power from the replacement power source, without interrupting power to the IHS.
Soft start circuits are used to limit surge currents to acceptable levels upon application of the voltage to un-energized capacitance banks in the IHS circuit. Examples of application of the voltage is when an energized AC power adapter is plugged into a portable IHS or when the IHS is placed in proximity of an inductive power/charging device, thereby causing the IHS to switch power sources from the battery to the newly connected external power source. In operation, the soft start circuit is to be reset prior to a reapplication of a new power source to the IHS to prevent circuit failure such as an adapter crowbar (e.g., output collapse) or soft start circuit failure. IHSs that are not configured to receive power from an inductive wireless power/charger device typically have an input charging capacitance of only a few hundred micro Farads (uFs). Accordingly, an RC time constant of approximately 10 mS for this type of device is used to slowly bias on a MOSFET switch to switch power sources, which limits the dv/dt. This, in turn, limits the input current inrush accordingly. When the AC power adaptor is removed, the RC time constant is self reset relatively quickly (˜10 mS), thus self resetting and becoming ready for reapplication of power by way of the relatively quick bleed-off time for the RC circuit (˜10 mS).
However, when using a wireless power/charger device to power the IHS, the IHS requires a significantly larger input bulk capacitance (e.g., ˜10,000 uF) on the primary input charging module. As such, this much larger bulk capacitance requires a much longer soft start period (e.g., ˜>500 mS) to limit the inrush current to acceptable limits due to the RC time constant for the circuit having the much larger capacitance. A problem with this is that the self reset time for the longer soft start period becomes proportionally much longer as well. With this longer reset time, removal and reapplication of an external power source, such as an AC power adaptor or a wireless power/charging device, can occur before the soft start circuit resets itself. If this happens, an AC adapter crowbar or soft start circuit failure is likely to occur due to an excessive inrush current, which cannot be slowed by the soft start circuit because the soft start circuit is not reset and ready to slowly transition between power sources.
The fast (e.g., ˜10 mS) soft start solution described above is simple and low cost and is therefore used for limiting inrush current in many portable IHSs. However, these systems are only well suited where RC time constants are small (e.g., <˜10 mS), such as IHSs that are not configured with a high input capacitance for receiving power from a wireless power/charger device. Other solutions, such as, dedicated soft start integrated circuits (ICs) having slew rate control, and current limit are available, however they are significantly more expensive.
Accordingly, it is desirable to provide an improved soft start system having an active reset.